Method of making a cover for an integrated optical circuit, cover for an integrated optical circuit, and integrated optical circuit made with this cover

ABSTRACT

A method for making a cover for an integrated optical circuit, a cover for an integrated optical circuit, and an integrated optical circuit made with this cover are proposed. The method serves to minimize the effort and expense in integrating optical components in fiberoptical systems. An optical element 29 is placed in a molding die (10) with adjusting elements (13) that adjust the optical component (29) in its position, and a curable liquid is cast all around the optical component (29), and after it solidifies, this liquid forms the cover (25).

BACKGROUND OF THE INVENTION

The invention relates generally to a method for making a cover for anintegrated optical circuit.

German Patent Application DE-P 42 12 208.2, MAYER/BOSCH, has alreadydisclosed a method for making optical polymer components with integratedfiber-chip coupling by a duplicate molding technique. To couple anintegrated optical circuit in between two glass fibers, a polymersubstrate is formed by means of a master structure such that the glassfibers come to rest in a V-shaped groove in the substrate. Theirlongitudinal axis is aligned with the longitudinal axis of a wave guidetrench located in the substrate between the V-shaped grooves. By fillingthe grooves and the wave guide trench with polymer adhesive, both amechanically firm bond between the substrate and the cover and anoptical coupling of the glass fibers to the wave guide formed of thepolymer adhesive are assured, once a polymer cover is put in place.

The article entitled "Channel glass wave guide detectors with graftedGaAs film in embedded configuration", in Electronic Letters 27 (1991),pp. 410-412, by Yi-Yan Chan et al, discloses the evanescent coupling ofa photodetector, grafted onto a glass substrate, to a wave guide locatedin the substrate. This production process requires precise adjustment ofthe wave guide and photo detector relative to one another, which must becarried out individually for each component and involves a complicatedadjustment process.

SUMMARY OF THE INVENTION

The method according to the invention has the advantage over the priorart that a cover for an integrated optical circuit can be made withextremely little effort for adjustment. There is also the advantage thatthe method of the invention is especially suitable for mass production,since the adjustment principle is automatable, and a plurality of coversfor integrated optical circuits can be made simultaneously, and aplurality of integrated optical circuits can also be made together inone cover all at once.

Forming the adjustment elements and the optical component with partlyoblique side faces is especially advantageous; as a result, even ifslight maladjustments occur, the optical component is automaticallyadjusted laterally by gravity. Another advantageous feature is theprovision of further adjustment elements that likewise automaticallyserve to provide vertical adjustment of the optical component.

Protrusions that leave behind a Bragg structure in the cover bring theadvantage that Bragg structures are jointly made at the same time thecover is made. Contacting of the chip contacts by recesses created inthe production process according to the invention advantageouslyeconomizes on one additional method step. Using a support plate not onlyfacilitates manipulation of the optical component but also permitssimultaneous production of a plurality of systems of the same type.Using a supplementary plate advantageously increases the mechanicalstability of the entire arrangement.

The cover according to the invention is in particular produced by themethod of the invention. V-shaped grooves facilitate the coupling ofglass fibers to a system that includes the cover. The production processis especially suitable for integrating both integrated photodetectorsand thermal actuators, because in that case, especially exact adjustmentis required, which is achieved with especially little effort and expenseby the method of the invention.

The cover of the invention is especially suitable for use in anintegrated optical circuit, and the wave guide is advantageously formedwhen the cover is joined to a substrate by means of the adhesive, whichfills a groove in the substrate.

DRAWING

Exemplary embodiments of the invention are shown in the drawing anddescribed in further detail in the following description. Shown are:

FIG. 1, a perspective, cutaway view of an integrated optical circuitwith a substrate, cover and glass fibers;

FIG. 2, a perspective view of the molding die and of the photodetectorto be placed in it;

FIG. 3, a cross section through the molding die with the photodetectorin place, the photodetector being wider than the spacing of theadjusting elements;

FIG. 4, a cross section through the molding die with the photodetectorin place, the photodetector being narrower than the spacing of theadjusting elements;

FIG. 5, a cross section through an integrated optical circuit having asubstrate and the cover in place, along with the photodetector and asupplementary plate;

FIG. 6, a plan view from below on the thermal actuator;

FIG. 7, a cross section through an integrated optical circuit having asubstrate and the cover in place, along with a thermal actuator;

FIG. 8, a perspective view of the molding die for making the cover withthe thermal actuator.

DETAILED DESCRIPTION OF THE EXEMPLARY EMBODIMENTS

FIG. 1 shows a perspective cutaway view of an integrated optical circuitwith a substrate 20, a cover 25, and glass fibers 34. The substrate 20preferably comprises a polymer (such as Plexiglass) and includes abottom plate 21 that has two V-shaped grooves 22 aligned with oneanother and one groove 23 of rectangular cross section, located betweenthe V-shaped grooves 22 with its longitudinal axis likewise aligned withthe longitudinal axis of the V-shaped grooves 22. The substrate 20 isjoined to the cover 25 by means of an optically transparent adhesive 24.The adhesive 24 is preferably also a polymer. The adhesive 24 fills thegroove 23 as well, and thus forms a wave guide 26. The cover 25 includesa cover plate 27, which has two further V-shaped grooves 28 on itsunderside, which once the cover 25 has been glued on come to restprecisely above the V-shaped grooves 22 of the substrate 20. An opticalcomponent 29 is also mounted in the cover plate 27. By way of example,the optical component 29 may be assumed to be a photodetector, which hasan absorption zone 30 on its underside. The photodetector 29 isseparated from the substrate 20 only by a thin fragmentary layer portion33 of the cover plate 27, and once the cover 27 has been glued on itcomes to rest with the absorption zone 30 directly above the wave guide26. Two connecting lines 31 extend between the substrate 20 and thecover 25 and continue in the form of two block-shaped recesses 32, whichare located in the layer portion 33 under the photodetector 29 parallelto the wave guide 26 and equidistant from it to the right and left,respectively; there, the recesses are conductively joined to twoelectrical contacts 18. The electrical contacts 18 extend between thelayer portion 33 and the photodetector 29 as far as the absorption zone30, where they serve to provide contacting of the absorption zone 30. Aglass fiber 34 is introduced into each of the V-shaped grooves 22 and28, each from one side. On its underside, the cover 25 also has fourindentations 35, whose shape is the complement to a gable shape, andwhich are likewise filled with the adhesive 24 and are each located onone corner of the photodetector 29.

In this arrangement, the photodetector 29 is evanescently coupled to thewave guide 26. Light traveling through the glass fibers 34 continues onits way through the wave guide 26 and again reaches the glass fibers 34,which continue onward. The wave guide 26, which is formed of theadhesive 24, has an index of refraction which is higher than that of thematerials for the cover plate 27 and the bottom plate 21 and whichshould be as nearly equal to the index of refraction of the glass fibers34 as possible, in order to keep optical losses slight. Thephotodetector 29 is suitable for detecting light in the wave guide 26and outputting a resultant detection signal to the connecting lines 31.The photodetector 29 is therefore positioned such that the absorptionzone 30 comes to rest precisely above the wave guide 26. This requiresprecise adjustment of the arrangement when it is assembled. The methodof the invention attains this object by means of a self-adjustingproduction process for the cover 25. To that end, for incorporation intothe cover 25, the photodetector 29 is adjusted via a molding die 10 (seeFIG. 2). The making of the cover 25, with the photodetector 29integrated with it, is done by casting a curable liquid into thearrangement comprising the molding die 10 and the photodetector 29. Thiscurable liquid is a liquid polymer, by way of example. After the curing,the molding die 10 is removed.

In FIG. 2, the molding die 10 for making the cover 25 is shown. Itincludes a base plate 11, on which two gable-shaped protrusions 15 andfour adjusting elements 13, in the form of gable-shaped protrusions areattached, which accordingly have oblique side faces 9. The fouradjusting elements 13 form the four corners of a rectangle, while thegable-shaped protrusions 15 are aligned with one another by their ridgeline and intersect the ridge line of the rectangle in the middle; thegable-shaped protrusions 15 are each located on one end outside therectangle. Parallel to the ridge line, the molding die 10 also has twofurther, block-shaped adjusting elements 14, which are located insidethe rectangle, respectively to the left and right equidistant from theridge line, and which has the function of spacer strips.

The adjusting elements 13 provide lateral centering and receive thephotodetector 29, whose underside thus comes to rest on the block-shapedfurther adjusting elements 14, as a result of which the photodetector 29is vertically adjusted. Ideally, the molding die 10 is made of nickel ina galvanic process.

FIG. 3 and FIG. 4 each show a cross section through an arrangement ofthe molding die 10 and the photodetector 29, in place, in the methodaccording to the invention for making the cover 25. The photodetector 29is secured by its top to a support plate 16. For the selection of thesupport plate material, copper, silicon, Teflon or ceramic is suitable,for instance. The photodetector 29 is partly beveled downward on allfour sides; that is, the photodetector 29 has four further oblique sidefaces 12, hereinafter called chamfers. The slope of the chamfers 12 isless than that of the oblique side faces 9 of the adjusting elements 13.Depending on the dimensions of the chamfers 12 and adjusting elements13, the photodetector 29 comes to rest in different ways on the moldingdie 10: if the chamfers 12 are higher than the adjusting elements 13,then the adjusting elements 13, with their ridge lines, touch thechamfers 12 along their sides, as shown in FIG. 3. If the chamfers 12are lower than the adjusting elements 13, then the adjusting elements 13touch the upper boundary edges of the chamfers 12 with their obliqueside faces 9 oriented toward the photodetector 29, as shown in FIG. 4.In each case, the photodetector 29 is dimensioned such that it sits withits underside on the block shaped further adjusting elements 14.

If the photodetector is made of indium phosphide or gallium arsenide,for instance, then an etching processing may be used to produce thechamfers 12 parallel to the wave guide 26, in which, with a surfacealignment of the detector crystal in the (100) direction, for instance,etching is done with an HCl solution in the (011) direction, whichproduces highly precise chamfers 12. The chamfers 12 at right angles tothe wave guide 26 may either be etched as well, or produced with a wafersaw; both of these processes produce less-accurate chamfers 12, sincethe process is not done in the (011) direction, although this has aneffect in the adjustment process only longitudinally of the wave guideand is thus tolerable. V-grooves and thus the chamfers 12 as well can beetched in all directions in the case of photodetectors made of silicon.After the positioning of the photodetector 29 in the molding die 10, theliquid polymer is cast onto the arrangement and fills all the voids inthe arrangement. The liquid polymer then cures into a rigid structurethat forms the cover 25. It is especially suitable to make the furtheradjusting elements in multiple parts, in order to reinforce the castingprocess.

The method for producing the cover 25 can be done in two ways:

1. After the photodetector 29 is secured to the support plate 16, thesupport plate 16 is placed in a liquid-polymer filled tub with the sideon which the photodetector 29 is secured facing upward, and then themolding die 10, likewise wetted with liquid polymer, is placed, roughlypreadjusted, in the tub in such a way that the adjusting elements 13automatically carry out the intended adjusting process. After the curingtime, during which a contact pressure is employed, the molding die 10 isremoved from the arrangement again. The support plate 16 can also beremoved.

2. Alternatively, the molding die 10 may act as the bottom of a tub, andthe photodetector 25 can be lowered onto it. Then the liquid polymer isintroduced, and the curing time is allowed to elapse before thearrangement is unmolded.

The block-shaped further adjusting elements 14 then leave behind theblock-shaped recesses 32 in the cover 25. The block-shaped recesses 32from the block-shaped further adjusting elements 14 serve in the nextmethod step to provide the connecting lines 31, in the form of contactholes for contacting the electrical contacts 18 of the photodetector 29.For that purpose, it is favorable to make the edges of the block-shapedfurther adjusting elements 14 oblique, in order to assure a secureelectrical contact when the connecting line material is provided. Theprovision of the connecting lines 31 after unmolding of the cover 25 issuitably done by a photolithographic etching process with ensuing metalcoating, such as sputtering. After the unmolding, the gable-shapedprotrusions 15 leave behind the further V-shaped grooves 28 in the coverplate 27, which when the integrated optical circuit is assembled serveto receive and adjust the glass fibers 34 that are to be put in place.Once the cover 25 has been made, then to assemble the integrated opticalcircuit, the cover 25 is glued to the substrate 20 by means of theadhesive 24; at the same time, the glass fibers 34 are placed in theintended V-shaped grooves 22, 28 and secured mechanically and optically,likewise by means of the adhesive 24, to the arrangement comprising thecover 25 and substrate 20. The indentations 35 of complementary shape toa gable that are left behind in the cover plate 27 in the moldingprocess, in the form of the inverse adjusting elements 13, are filledwith the adhesive 24 when the cover 25 and substrate 20 are joinedtogether for the integrated optical circuit, and have no furtherfunction. The block-shaped recesses 32, left behind in the cover plate27 after unmolding by the block-shaped further adjusting elements 14, bymeans of which recesses the electrical contacts 18 are joined to theconnecting lines 31 in the next method step, are filled with theadhesive 24 in the ensuing gluing, which serves to assemble theintegrated optical circuit.

FIG. 5 shows a cross section through the integrated optical circuit withthe cover 25 on the substrate 20, using a supplementary plate 17. Thecover 25 is glued to the substrate 20, which includes the wave guide 26.The cover includes the photodetector 29, which is embedded in-the coverplate 27 and is joined on its top to the complementary plate 17. Thesupplementary plate 17 is secured by its top to the support plate 16.The absorption zone 30 on the underside of the photodetector 29 isseparated from the substrate 20 by the layer portion 33. The electricalcontacts 18 are joined to the connecting lines 31, which extend throughthe block-shaped recesses 32 that were created in the cover 25 by theblock-shaped further adjusting elements 14. The connecting lines 31extend onward to the outside between the cover 25 and the substrate 20.In this case, the support plate 16 was not removed from the arrangementafter solidification of the liquid polymer. The supplementary plate 17between the photodetector 29 and the support plate 16 is larger in itsoutside dimensions than the photodetector 29 and smaller than thesupport plate 16. The supplementary plate 17 serves to make the cover 25thicker, which thereby becomes mechanically more stable.

For improved function, it is possible to metallize the underside of thephotodetector 29 over as large an area as possible, in order to preventthe electromagnetic field carried in the wave guide 26 from penetratingthe photodetector 29, which would mean increased wave guide losses. Onthe other hand, since the metallizing has a disruptive influence on thepropagation of light in the wave guide 26, it is suitable to increasethe spacing between the metallizing of the photodetector 29 and the waveguide 26. This can be done by increasing the height of the furtheradjusting elements 14. To compensate for the then-increased spacingbetween the absorption zone 30 and the wave guide 26 as well, it issuitable for the photodetector 29 to have a protrusion on the face ofthe underside, located between the further adjusting elements 14 and onwhich the absorption zone 30 is also located, which protrusion ispreferably of the same material as the photodetector 29 and whose taskis, because of its higher index of refraction, to improve theoutcoupling of light from the wave guide 29 to the absorption zone 30.

As a further application, the integration of a further optical component35 in the form of a thermal actuator is contemplated. Once again,adjustment of the thermal actuator 36 is already done by means of themolding die 10 in the production of the cover 25 into which the thermalactuator 36 is to be integrated. The layout of the substrate 20 and thearrangement of glass fibers 34 and of the wave guide 26 are thereforethe same as described above.

FIG. 6 shows a thermal actuator 36 with a hot wire 19 in a plan viewfrom below. The hot wire 19 is secured to the underside of the thermalactuator 36, has two further electrical contacts 37 as terminals, andserves the purpose of thermal control of the thermally sensitive waveguide 26 formed of the adhesive 24.

FIG. 7 shows a cross section through an arrangement comprising thesubstrate 20 and cover 25 with the thermal actuators 36 having the hotwire 19. The thermal actuator 36 is secured by its top to the supportplate 16 and on its underside has the further electrical contacts 37 andthe hot wire 19. Once the cover 25 is glued in place, the hot wire 19comes to rest precisely above the wave guide 26. On the underside, thesubstrate 20 is joined to a cooling plate 8.

Current flowing through the hot wire 19 generates heat, and a result thehot wire 19 heats its immediate surroundings, and in particular the waveguide 26. The cooling plate 8, acting as a heat sink, is provided inorder to dissipate the heat; it is thermally conductively secured to theunderside of the substrate 20. It is equally possible to secure thecooling plate 8 thermally conductively to the top of the cover 25. Byintegrating the thermal actuator 36 into the course of the light carriedby means of the glass fibers 34 and the wave guide 26, a light signalcan be thermooptically varied in the wave guide 26, since the wave guide26 has a temperature-dependent index of refraction.

FIG. 8 is a perspective view of the molding die 10 for making the cover25 with the thermal actuator 36 having the hot wire 19. The molding die10 in FIG. 7 differs from the molding die 10 in FIG. 2 only in thearrangement and form of the block-shaped further adjusting elements 14.Here, instead of the block-shaped further adjusting elements 14, themolding die 10 has spacers 38, which are arranged in the pattern of thedots on the "B" side of dice on the surface of the base plate 11, insidethe rectangle formed by the gable-shaped adjusting elements 13. When athermal actuator with a hot wire 19 is integrated, the demands forexactness of adjustment of the hot wire 19 in the vertical direction arenot so stringent, and it is therefore sufficient for the spacers to besimple glued-on sheet-metal disks, or galvanically grown protrusions.

We claim:
 1. A method of making a cover for an integrated opticalcircuit, which has a substrate in which a wave guide is integrated,characterized in that the cover (25) includes an optical component (29),and that a molding die (10) is provided that has adjusting elements(13), which when the optical component (29) is placed on the molding die(10) determine the lateral position of the optical component (29), andthat the cover (29) is made by casting a curable liquid all around theoptical component (29).
 2. The method of claim 1, characterized in thatthe adjusting elements (13) and the optical component (29) have at leastpartially oblique side faces (12, 9), which slide on one another whenthe optical component (29) is placed on the molding die (10).
 3. Themethod of claim 1, characterized in that the molding die (10) hasfurther adjusting elements (14), which reinforce the optical component(29) from below as it is put in place.
 4. The method of claim 1,characterized in that the molding die (10) has molding elements thatleave a Bragg structure behind in the cover (25).
 5. The method of claim3, characterized in that after unmolding of the molding die (10),electrically conductive material is applied to portions of the undersideof the cover (25), and that the optical component (29) has electricalcontacts (18), which are conductively joined to the electricallyconductive material by means of recesses (32), created in the methodstep of the casting of the further adjusting elements (14), located onthe molding die (10), using the curable liquid.
 6. The method of claims1, characterized in that the optical component (29), before being placedon the molding die (10), is secured by its top to a support plate (16).7. The method of claim 6, characterized in that a supplementary plate(17) is located between the optical component (29) and the support plate(16).
 8. A cover for an integrated optical circuit, characterized inthat the cover (25) includes an optical component (29), and that thecover (25) has indentations (35) that are located all around the opticalcomponent (29), wherein the optical component (29) is an integratedthermal actuator.
 9. The cover of claim 8, characterized in that thecover (25) has V-shaped grooves (28), which serve as guide elements forglass fibers (34).
 10. The cover of claim 8, characterized in that theoptical element (29) is a photodetector.
 11. An integrated opticalcircuit having a cover, wherein the cover includes an optical componentcomprised of an integrated thermal actuator, V-shaped grooves (28), andindentations that are located all around the optical component, andwherein the integrated optical circuit includes a substrate (20), whichhas at least two V-shaped grooves (22) and one groove 23 located betweenthe two V-shaped grooves (22), the cover (25) with the optical component(29) being secured to the substrate (20) by means of an opticallytransparent adhesive (24), wherein the optically transparent adhesive(24) simultaneously fills the groove (23), thereby forming a wave guide(26), and the V-shaped grooves (28) of the cover (25) being locatedabove the V-shaped grooves (22) of the substrate (20).